From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752639AbaCFL7Q (ORCPT ); Thu, 6 Mar 2014 06:59:16 -0500 Received: from mailout2.w2.samsung.com ([211.189.100.12]:20817 "EHLO usmailout2.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751978AbaCFL7O (ORCPT ); Thu, 6 Mar 2014 06:59:14 -0500 X-AuditID: cbfec372-b7fa96d000006a7b-7b-53186311efdc Date: Thu, 06 Mar 2014 08:59:07 -0300 From: Mauro Carvalho Chehab To: Laurent Pinchart Cc: Greg Kroah-Hartman , Joe Perches , devel@driverdev.osuosl.org, Paul Bolle , linux-kernel@vger.kernel.org, linux-media@vger.kernel.org Subject: Re: [PATCH v2] [media] v4l: omap4iss: Add DEBUG compiler flag Message-id: <20140306085907.0e4bc30a@samsung.com> In-reply-to: <6116451.L9roNDfSqL@avalon> References: <1391958577.25424.22.camel@x220> <2136780.FIdBGb725A@avalon> <20140306044529.GA6466@kroah.com> <6116451.L9roNDfSqL@avalon> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-redhat-linux-gnu) MIME-version: 1.0 Content-type: text/plain; charset=US-ASCII Content-transfer-encoding: 7bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFjrCLMWRmVeSWpSXmKPExsVy+t/hEF3BZIlggx9n2S32nPnFbtG8eD2b xez7j1ksOicuYbe4vGsOm0XPhq2sFotunWF2YPe4t+8wi8fsjpmsHvvnrmH3+LLqGrPHxu1P mDw+b5ILYIvisklJzcksSy3St0vgylgx5RFjwSeRiiW/e1gaGI8KdDFyckgImEhsaelgg7DF JC7cWw9kc3EICSxhlHjwp4MZwulmklh+7Cx7FyMHB4uAqsTbmdwgDWwCRhKvGltYQWwRAQuJ 3kXTGUHqmQUuMEo0/V/DApIQFnCTWNkzix3E5hUwlJjeehTM5hTQkLg46SbUgg5Gif8f+9gh znCSePV6MhNEg6DEj8n3wAYxC2hJbN7WxAphy0tsXvOWeQKjwCwkZbOQlM1CUraAkXkVo2hp cXJBcVJ6rqFecWJucWleul5yfu4mRkjIF+1gfLbB6hCjAAejEg/vBj/xYCHWxLLiytxDjBIc zEoivFsMJYKFeFMSK6tSi/Lji0pzUosPMTJxcEo1MLpfKPrwrKNrqdfq70tWn5xlvWbyHad6 lsudyTZTXtbZPf9zzLv3Q23n7bwyCw4jjStFp8QjIjOU2xOEIwI4uB9xCr5mZnHn2bhr2hvv 2VNcrdmyLgbenuH5MnXXQ9HKdJH7eydafBTpK/3XbiDXfeTOjdXb57nZ7Dzwpapug/ADV+1N Dz98yFBiKc5INNRiLipOBACCuQu3VwIAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Thu, 06 Mar 2014 12:00:30 +0100 Laurent Pinchart escreveu: > Hi Greg, > > On Wednesday 05 March 2014 20:45:29 Greg Kroah-Hartman wrote: > > On Thu, Mar 06, 2014 at 01:48:29AM +0100, Laurent Pinchart wrote: > > > On Wednesday 05 March 2014 16:28:03 Joe Perches wrote: > > > > On Thu, 2014-03-06 at 00:50 +0100, Laurent Pinchart wrote: > > > > > Please note that -DDEBUG is equivalent to '#define DEBUG', not to > > > > > '#define CONFIG_DEBUG'. 'DEBUG' needs to be defined for dev_dbg() to > > > > > have any effect. > > > > > > > > Not quite. If CONFIG_DYNAMIC_DEBUG is set, these > > > > dev_dbg statements are compiled in but not by default > > > > set to emit output. Output can be enabled by using > > > > dynamic_debug controls like: > > > > > > > > # echo -n 'file omap4iss/* +p' > /dynamic_debug/control > > > > > > > > See Documentation/dynamic-debug-howto.txt for more details. > > > > > > Thank you for the additional information. > > > > > > Would you recommend to drop driver-specific Kconfig options related to > > > debugging and use CONFIG_DYNAMIC_DEBUG instead ? > > > > Yes, please do that, no one wants to rebuild drivers and subsystems with > > different options just for debugging. I agree that this is the best solution. > > Is CONFIG_DYNAMIC_DEBUG lean enough to be used on embedded systems ? Note that > people would still have to rebuild their kernel to enable CONFIG_DYNAMIC_DEBUG > anyway :-) Some distros, like Fedora, ships two different kernels: one compiled with most of those DEBUG macros disabled, and another one with them enabled: kernel.x86_64 : The Linux kernel kernel-debug.x86_64 : The Linux kernel compiled with extra debugging enabled That helps to have a "production" kernel using less memory, yet allowing one to boot with the debug Kernel, if he needs to debug some driver(s). PS.: In Fedora, in the specific case of CONFIG_DYNAMIC_DEBUG, it has it enabled since, at least, 2010 (when they changed the SCM to git) at the "production" kernel even for ARM. So, I suspect that the extra amount of memory required for it is not much, but I never actually bothered to check. On my view, except on embedded systems with very very limited memory constraints, it makes sense to keep CONFIG_DYNAMIC_DEBUG always enabled. Btw, I would expect a reasonable amount of RAM on any embedded system that supports v4l, because video buffers require a lot of memory. Comparing to the size of those buffers, I suspect that the extra amount of memory for the debug strings and code is negligible. -- Cheers, Mauro